STRUCTURED POLYCYCLIC PEPTIDE

1 . A peptide ligand comprising a polypeptide linked to a molecular scaffold at n attachment points, wherein said polypeptide is cyclised and forms n separate loops subtended between said n attachment points on the molecular scaffold, wherein n is greater than or equal to 2.

2 . The peptide ligand of claim 1 , wherein the polypeptide is cyclised by N- to C-terminal fusion.

3 . The peptide ligand of claim 1 , wherein the polypeptide is cyclised after attachment to the molecular scaffold.

4 . The peptide of claim 1 , wherein the polypeptide is cyclised by N-C crosslinking or deprotection of a protected N α or C α derivatised amino acid to couple said amino acid to the opposite terminus of the polypeptide.

5 . The peptide ligand of claim 1 , wherein the polypeptide is cyclised by enzymatic means.

6 . The peptide ligand of to claim 5 , wherein the enzyme is a transglutaminase.

7 . The peptide ligand of claim 6 , wherein the transglutaminase is a microbial transglutaminase.

8 . The peptide ligand of claim, wherein the polypeptide incorporates an N- and/or C-terminal substrate sequence for the enzyme.

9 . The peptide ligand of claim 1 , which is capable of binding to more than one separate target.

10 . The peptide ligand of claim 9 , wherein the loop formed by polypeptide cyclisation binds to a target which is different to that bound by at least one other loop.

11 . The repertoire of peptide ligands of, claim 1 .

12 . The repertoire of claim 11 , which is displayed using a genetic display system.

13 . The repertoire of claim 12 , wherein the genetic display system is phage display.

14 . The repertoire of claim 11 , which is naive.

15 . The repertoire of claim 11 , which has been selected for binding to one or more targets.

16 . The repertoire of claim 15 , wherein the selection for binding to the one or more targets is carried out before cyclisation.

17 . A method for preparing a peptide ligand of claim 1 , comprising the steps of:

(a) providing one or more peptide ligands, wherein the polypeptide comprises n reactive groups which form a covalent linkage to n attachment points on the molecular scaffold, n-1 loops which comprise a sequence of two or more amino acids subtended between said n reactive groups, and wherein neither the most N- or C-terminal reactive group is comprised in an N- or C-terminal amino acid;

(b) joining the free N- and C-termini of the polypeptide to create a cyclic polypeptide, thus forming an nth loop.

18 . The method of claim 17 , further comprising selecting the peptide ligands for binding to a target.

19 . The method of claim 18 , comprising the steps of:

(a) providing one or more peptide ligands, wherein the polypeptide comprises n reactive groups which form a covalent linkage to n attachment points on the molecular scaffold, n-1 loops which comprise a sequence of two or more amino acids subtended between said n reactive groups, and wherein neither the most N- or C-terminal reactive group is comprised in an N- or C-terminal amino acid;

(b) selecting said peptide ligands for binding to a target;

(c) joining the free N- and C-termini of the polypeptide in the peptide ligands selected in (b) to create a cyclic polypeptide, thus forming an nth loop; and

(d) selecting the cyclised peptide ligands for binding to the target.

20 . A method of claim 19 , wherein, after step (c), binding of the peptide ligand to the target is improved.

21 . A method for preparing a multispecific peptide ligand, comprising the steps of:

(a) providing one or more peptide ligands, wherein the polypeptide comprises n reactive groups which form a covalent linkage to n attachment points on the molecular scaffold, n-1 loops which comprise a sequence of two or more amino acids subtended between said n reactive groups, and wherein neither the most N- or C-terminal reactive group is comprised in an N- or C-terminal amino acid;

(b) selecting said peptide ligands for binding to a first target;

(c) joining the free N- and C-termini of the polypeptide in the peptide ligands selected in (b) to create a cyclic polypeptide, thus forming an nth loop; and

(d) selecting the cyclised peptide ligands for binding to a second target.

22 . The method of claim 17 , wherein the cyclised peptide ligand is further modified by

(a) amino acid side chain modification or substitution; or

(b) polypeptide backbone alteration.

23 . The method of claim 22 , wherein the backbone modification is selected from the group consisting of introducing, near the site of protease cleavage, a D-amino acid, a reduced peptide bond, and N-methylation.

24 . The method of claim 22 , comprising the steps of:

(a) providing one or more peptide ligands, wherein the polypeptide comprises n reactive groups which form a covalent linkage to n attachment points on the molecular scaffold, n-1 loops which comprise a sequence of two or more amino acids subtended between said n reactive groups, and wherein neither the most N- or C-terminal reactive group is comprised in an N- or C-terminal amino acid;

(b) selecting said peptide ligands for binding to a target;

(c) joining the free N- and C-termini of the polypeptide in the peptide ligands selected in (b) to create a cyclic polypeptide, thus forming an nth loop;

(d) modifying the cyclised ligands by amino acid side chain modification or substitution, or backbone alteration;

(e) selecting the cyclised peptide ligands for binding to the target; and

(f) optionally, repeating steps (d) and (e).

25 . The repertoire of claim 15 , wherein the selection for binding to the one or more targets is carried out after cyclisation.

26 . The repertoire of claim 15 , wherein the selection for binding to the one or more targets is carried out both before and after cyclisation.